The present invention relates to a trial medical implant device, and more particularly, to a trial medical implant device for evaluating the size, shape, and alignment of the implant with respect to an anatomical structure. The present invention also relates to a method of manufacturing a trial implant device.
Advancing age, as well as injuries, can lead to changes in the various bones, discs, joints and ligaments of the body. In particular, these changes can manifest themselves in the form of damage or degeneration of an intervertebral disc, the result of which is mild to severe chronic back pain. Intervertebral discs serve as xe2x80x9cshockxe2x80x9d absorbers for the spinal column, absorbing pressure delivered to the spinal column. Additionally, they maintain the proper anatomical separation between two adjacent vertebra. This separation is necessary for allowing both the afferent and efferent nerves to exit and enter, respectively, the spinal column.
Treatment for a diseased or damaged disc can involve the removal of the natural, damaged disk tissue, and the subsequent replacement of the disc with an implant, such as an interbody cage or fusion device, or a disc prosthesis. The implant should have an appropriate size and shape to complement the normal height of the disc and to contour the vertebral endplates adjacent the disc space to provide stability and, if a fusion device is being implanted, to promote fusion. If the shape of the vertebral endplates does not match the shape of the implant, shifting can occur resulting in misalignment of the vertebrae. Accordingly, it is important for the implant to correspond as closely as possible to the region of the intradiscal space that is receiving the implant.
Selection of a properly sized implant can be difficult due to the enclosed nature of the nucleus cavity. X-rays generally reveal very little about the particular size and shape of the intradiscal space, and thus surgeons often have to rely on an estimated shape and size based on physiological factors, such as the patient""s height, weight, etc., as well as the position of the vertebrae. While this method can be sufficient, the selection of an improperly sized implant can lead to problems. An oversized implant, for example, will be difficult to position between the adjacent vertebrae and can lead to long term problems once implanted. Moreover, due to the enclosed nature of the nucleus cavity, it is virtually impossible for a surgeon to accurately evaluate the size and shape of the cavity, much less the matching of the implant with the vertebral endplates. Unfortunately, the sizing problem is not always discovered until the surgeon attempts to position the implant between the vertebrae. As a result, the implant will have been in direct contact with bodily fluids and will be contaminated. Some implants can be virtually impossible to resterilize due to the nature of the materials from which they are made. In such cases, it is necessary to discard an expensive device.
To overcome this problem, trial implants and trial implant kits have been developed to assist surgeons in selecting an implant having the appropriate size and shape. U.S. Pat. No. 6,113,639 of Ray et al. discloses, for example, a trial implant kit containing several trial implants, each sized and shaped to simulate the size and shape of an available prosthetic implant. The surgeon can select an implant from the kit to temporarily position within the disc space to evaluate the size of the intradiscal space and the fit of a sample prosthesis. A contrast material can be injected into the nucleus cavity to view the trial implant with respect to the intradiscal space via a fluoroscope.
While fluoroscopy or x-ray can be effective to verify the placement of a trial implant, the image produced can be distorted by the large, opaque implant. This distortion can either shield or completely obscure the anatomical matching that the surgeon desires to verify. It can also be difficult to accurately assess whether the implant is in close contact with the complex geometries of the adjacent vertebral endplates.
Accordingly, there is a need for a trial implant that can be used to accurately and effectively evaluate the size, shape, and alignment of the implant with respect to an anatomical structure.
The present invention provides a trial implant and trial implant kit for assisting a physician in selecting an appropriately sized prosthesis. In one embodiment, the trial medical implant device includes a body formed from a radio-lucent material and having a size and shape adapted to fit within or adjacent to an interstitial space, and at least one marker associated with the body and formed from a radio-opaque material. The at least one marker is configured to provide an x-ray visible reference to indicate the position and alignment of the body with respect to an anatomical structure when the trial medical implant device is positioned within an interstitial space.
The markers can be disposed on an outer surface of the body and/or embedded in the body. In one embodiment, the implant includes several markers, each of which can be selectively positioned to intersect to form one or more reference points on the body. Thus, when implanted in the body, an x-ray image can be used to determine the exact position of the implant with respect to an anatomical structure. In another embodiment, the implant can include first and second markers that are selectively distinguishable on an x-ray image. Each marker can have a variety of shapes, and can be in the form of a tube, cross, sphere, plate, ring, rod, T-shape, and combinations thereof.
In further aspects of the present invention, the body of the implant has a shape and size adapted to fit between adjacent vertebral bodies. By way of non-limiting example, the body can be a disc-shaped member having a superior, bone-contacting surface and an inferior, bone-contacting surface. The at least one marker is preferably effective to indicate the alignment of the superior and inferior bone-contacting surfaces of the body with respect to superior and inferior endplates of adjacent vertebral bodies when the implant is positioned between adjacent vertebral bodies.
In another embodiment of the present invention, a trial spinal implant is provided having a trial implant member formed from a radio-lucent material and having a size and shape configured to fit between adjacent vertebral bodies. The trial implant member includes a superior bone-contacting surface and an inferior bone-contacting surface. At least one marker formed from a radio-opaque material is associated with the trial implant member such that, when the trial implant is positioned between adjacent vertebral bodies, the at least one marker provides at least one x-ray visible reference to indicate the position and/or alignment of the implant with respect to the adjacent vertebral bodies. In a preferred embodiment, the superior and inferior bone-contacting surfaces of the trial implant member each have a shape adapted to conform to an endplate of an adjacent vertebral body. Thus, when implanted in the body, the at least one marker indicates, on an x-ray image, the alignment of the superior and inferior bone-contacting surfaces of the trial implant member with respect to the endplates of adjacent vertebral bodies.
In yet another embodiment of the present invention, a trial implant system is provided having a plurality of implantable trial prostheses. Each implantable prosthesis includes a body formed from a radio-lucent material and having a size and shape adapted to fit within or adjacent to an anatomical structure, and at least one marker associated with the body and formed from a radio-opaque material. The at least one marker is configured to provide an x-ray visible reference to indicate the position and alignment of the body with respect to the anatomical structure when the implantable trial prosthesis is positioned within or adjacent to an anatomical structure.
In other aspects of the present invention, a method for manufacturing a trial implant is provided. The method includes the steps of providing at least one marker formed from a radio-opaque material, providing a mold having a desired size and shape for a medical implant, strategically placing each of the at least one markers in the mold such that the markers are configured to provide at least one x-ray visible reference to indicate the size and shape of the medical implant, and injecting a radio-lucent material into the mold to form a trial implant.